is bitfinex funding safe and are we guaranteed that we can get our investment back plus the interests?
No.
Nothing is guaranteed.
True but still that's not the question here. The answer to Op's question is "yes".
The question that I quoted and responded to was answered correctly. The answer being "No".
"No" in that lending at Bitfinex cannot be qualified as safe (what is safe?), and that he isn't guaranteed anything.
With the same perspective and meaning of yours, you should go and take anything that you have in a bank and put them under your bed.
But then again, is it safe there? No...
The question isn't for a philoshopical debate/discussion. So until Bitfinex crashes or declare bankruptcy or get a meteor in their head offices (!) the answer will be "Yes".
Anyone that will put funds for lending on their platform, will get his capital plus the interest that he will put.